A Warrnambool Fire Brigade spokesman said when workers arrived at 7am to shed five at Silverton Park the electrical switchboard was smoking.

Old wiring is believed to be the cause of the smoke.

It's expected the switchboard, valued at about $5000 will be replaced by a modern appliance.

"The Fresha employees did a good job. They had used an extinguisher to bring the fire under control after arriving at work to find the shed full of smoke," he said.